Turbine bucket



0. JUNGGREN TURBINE BUCKET April 16, 1935.

Filed Sept. 30, 1933 Inventor: Oscar" Ju'nggren,

His Attorney.

Patented Apr. 16, 1935,

UNITED STATES TURBINE BUCKET Oscar Junggren, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application September 30, 1933, Serial No. 691,647

3 Claims.

The present invention relates to buckets for elastic fluid turbines usually comprising a base and a blade having an elongated form and, broadly speaking, a crescent-shaped cross-section decreasing in area from its inner to its outer end. In the design of long buckets for the last stage or stages of elastic fluid turbines attention must be paid to the high centrifugal forces to which the buckets are subjected, and also to the wear, corrosion and erosion of the bucket-material caused by wet steam. Owing to the fact that the wet steam flows mainly through the outer region of the turbine, the outer portions of the buckets are subjected more to the injurious effects of wet steam or like elastic fluid than the inner portions.

The object of my invention is to provide an improved construction for buckets whereby the injurious effect of wet steam or the like on the outer blade portions as well as the great centrifugal forces acting on said outer-portions are considerably reduced.

For a consideration of what I believe to be novel and my invention, attention is directed to the following description and the claims appended thereto in conection with the accompanying drawing.

In the drawing I have shown a perspective view, partly broken away, of two buckets embodying my invention.

Each bucket comprises a base l0 and a blade I I. The base is dovetail shaped and held in a groove l2 of a rim or disk l3. In accordance with my invention I make the blade of two portions, an

inner portion H and an outer portion ii. The inner portion I4 is solid or massive and integrally formed with the base It and made of forged or rolled steel or alloy. The outer end of the inner portion I4 is reduced in cross section to form a shoulder l6 and a projection ll.

The outer portion I5 is hollow and made of an extremely hard material with high resistivity against wear by steam or like elastic fluid. Preferably I make the outer portion from a material generally known as Stellite which is a composition of 34-75% cobalt, 13-36% chromium and 540% of tungsten and/or molybdenum. Stellite sheet metal is pressed or punched in two parts welded together at their edges l8 and IS. The lower end of the outer portion l5 telescopes the projection l1 and is seated against the shoulder ii of the inner portion. The two portions are welded or brazed together as in icated by a weld 20. A plug 2| is inserted in the outer end of the hollow portion l5 and fastened thereto by a weld 22. The plug has a projection 23 to be inserted into a shroud band 26 for holding the outer ends of a plurality of buckets together.

My improved bucket has two important advantages, namely, flrst, its outer portion is light, thereby reducing the centrifugal forces transferred from the outer portion to the inner portion to a minimum, permitting the inner portion to be made with a smaller cross-section than necessary were the outer portion solid or massive; and second, the outer portion being made of Stellite or like material is little affected by wet steam. The manufacture of the outer portion by pressing a sheet of Stellite over a die having the shape of the hole defined by the finished outer portion is very' simple and less expensive than the manufacture of a solid portion The light outer portion of the blade permits the use of a larger blade which by decreasing the velocity loss of the steam or like elastic fluid from the last wheel will cause an increase in efliciency of the turbine. Also, if the efficiency is kept constant, the capacity of a turbine can be increased for a given speed. This permits the cost per kilowatt of a turbine to be decreased, as the last wheel, in general, determines the limitation in the capacity for a given speed.

What I claim as new and desire to secure by Letters Patent of the United States is:

I 1. A turbine bucket having a blade comprising an inner solid .portion having a reduced outer end forming a shoulder and an outer hollow portion made from sheet metal and welded to the reduced end of the inner portion, the outer surface of the outer portion forming a smooth continuation of the outer surface of the inner portion. v

2. A turbine bucket having a blade comprising an inner solid portion made from steel and having a reduced outer end forming a shoulder, and an outer hollow portion made from a sheet material harder than steel telescoping the reduced end of the inner portion and being united therewith, the outer surface of the outer portion forming a smooth continuation of the outer surface of the inner portion.

3. A turbine bucket having a base and a blade, the blade comprising an inner solid portion int'egrally formed with the base, the outer end of the inner portion being reduced to define a. shoulder, and an outer hollow portion made of sheet metal with a resistivity against corrosion greater than theresistivity of the material forming the inner portion, the inner end of the outer portion facing the shoulder defined by the reduced outer end of the inner portion and being united therewith, the outer surface of the outer portion forming a smooth continuation of the outer surface of the inner portion.

OSCAR JUNGGREN. 

